<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<input type="text" id="n1">
<input type="text" id="n2">
<input type="button" value="加" onclick="f(1)">
<input type="button" value="减" onclick="f(2)">
<input type="button" value="乘" onclick="f(3)">
<input type="button" value="除" onclick="f(4)">
<div></div>
<script>
    function f(x){
        let i = document.querySelector("#n1");
        let j = document.querySelector("#n2");
        let d = document.querySelector("div");
        if (isNaN(i.value)){
            d.innerText="输入错误"
            return;
        }
        switch (x) {
            case 1:
                d.innerText=i.value*1+j.value*1;
                break;
            case 2:
                d.innerText=i.value*1-j.value*1;
                break
            case 3:
                d.innerText=i.value*1*j.value*1;
                break;
            case 4:
                d.innerText=i.value*1/j.value*1;
                break;
        }


    }

</script>
</body>
</html>